Improved surveying-compasses



G. W. DICKINSON, Jr.

Surveyors Compass. No. 27,210. I Patgnted Feb. 21, 1860.

UNITED STATES PATENT Genres.

GEO. WV. DICKINSON, JR, OF BRECKENRIDGE, VIRGINIA.

IMPROVED SURVEYlNG-COMPASSES.

Specification forming part of Letters Patent No. 27,210, dated February21, 1860.

To all whom it may concern:

Be it known that l, GEORGE W. DICKINSON, Jr., of Breckenridge, in thecounty of Henry and State of Virginia, have invented a new and ImprovedSurveyors Compasses; and I do hereby declare that the following is afull, clear, and exact description of the same, reference being had tothe accompanying drawings, forming a part of this specification, inwhich- Figure 1 represents a plan or top View of my invention. Fig. 2 isa side elevation of the same.

Similar letters of reference in both views indicate corresponding parts.

The object of this invention is to arrange a surveyors compasses in suchamanner that the same, by means of a series of adjustable scales, servesto solve all triangles, and consequently all rectilinear figures, whichmay occur in the various operations of a surveyor, and to facilitate thedrawing of the same.

This object is obtained by arranging on the base of the mainsemicirolean additional semicircle, the base-line of which coincideswith or is parallel to the base-line of the frame on which the mainsemicircle turns, and which has a double sliding motion, one in thedirection of the base-line and the other at right angles to it. A scalethat slides in and turns with a pivot in the center of the additionalsemicircle, together with a scale turning on the center of the mainsemicircle and scales marked on the base-line of the frame as well asthat of the main semicircle, serves to solve the various triangles whichmay occur, as will be hereinafter more fully explained.

To enable those skilled in the art to make and use my invention, I willproceed to describe its construction and operation.

A represents a semicircular frame, arranged with sockets (6 b to fit ona pivot supported by a common three-legged standard, such as aregenerally usedforsurveyorsinstruments. The socket a is used when it isdesired to use the compasses in ahorizontalposition, and the socket 1)is used when it is desired to take altitudes. A needle, B, and aspirit-level serve to bring the compasses into the required position.

The frame A supports a semicircle, O, the center of which coincides withthe center of the frame A, and which turns on a pivot, 0, in thiscenter. The base of this semicircle is prolonged beyond the frame A, sothat a line drawn through them coincides exactly with the base-line ofthe frame. By means of these sights, therefore, and by the aid of theneedle B, the base-line can be brought in any desirable direction, andthe angle which another line makes with this base-line is determined byturning the semicircle 0 until a line drawn through the sights Dcoincides or is parallel with said line, and in order to be able toascertain the number of degrees of such angles the semicircular side ofthe frame A is divided into one hundred and eighty degrees, in the usualmanner.

The base-line of the frame A and also that one of the semicircle G areboth marked with like indications, commencing in the center, so

as to form scales 0 and f, each mark on which indicates a foot, or ayard, or a pole, or any known distance; and on the top of thesemicircle, aud turninginitscenter, is the additional scale g, furnishedwith marks equal to the marks on the scales 6 and f.

F is the additional semicircle, that slides on a bar, G, at right anglesto the baseline ofthc frame A. The bar G is secured to a slide, H, whichmoves in a groove in the side of the frame A and parallel to itsbase-line. The center of the additional semicircle F is provided with aswivel-head, I, which turns in the cerr ter of said semicircle, andwhich serves as a socket for the sliding scale h. The marks on thisscale are equal to the marks on the scales c,f, and g, and thesemicircle F is divided into one hundred and eighty degrees, so that theangle of the scale It with the base-line of the frame can always beascertained. The bar G, which I denominate the protractor, is alsofurnished with a scale equal to the scales 6,],-

g, and h, so that the distancev of the additional semicircle F from thebase-line of the frameA or the distance at which the scale 9 intersectswith the protractor G can be ascertained at a glance.

The operation is as follows: A triangle can be determined ifthefollowingparts are known, first, the three sides; second, two sidesand the iuclosed angle; third, two sides and the angle opposite to thelargest of the two known sides; fourth, one side and two angles. Inorder to determine a triangle by the aid of my compasses, if the threesides are known, one being forty, the other forty, and the thirdtwenty-five poles, place the compass before you, shift the additionalsemicircle l and the scale It until it intersects the scale 0 at 40, andpush the scale It out until the mark 25 on the same coincides with themark 40 on the scale e, and turn the semicircle O and the scale h,always, however, keeping the mark 25 on the mark 40 of the scale 0,until the mark 40 on the scale f coincides with the scale h, and thetriangle is ready. The angle between the scales cand f is determined bythe division on the additional semicircle F, giving the number ofdegrees of the third angle by subtracting the sum of the twoformerangles from onehundred and eighty degrees, so that all the piecesof the triangle are known. Theheight of the triangle is found byshifting the semicircle F and by turning the scale h, always keeping itsend on the mark 40 of the scalefuntil it stands at right angles with thescale 0, and the point at which the scale It intersects with the scale 0gives the height. By multiplying the height with onehalf of thebase-line the area of the triangle is found. If two sides of thetriangle are given, together with the inclosed angle-one side to besixty poles, the other titty poles, and the angleto he thirty degreesandit is desired to find the other parts, turn the semicircle C until thescalefincloses an angle of thirty degrees with the scale 6, and theslide it is now shifted until it intersects with the scale 0 at the mark60 and with the scale fat the mark 50. The length of the third side isnow given by the scale it, and the angle inclosed by the scales 6 and his found by the intersection of the scale It with the division on theadditional semicircle F. From these two examples it will be understoodhow, bythe aid of my compasses, every triangle may be determined it asut'fieient quantity of its parts are known. In many cases it will befound more convenient to use the scales f, g, and it instead of thescales e,f, and h, and in many cases itbecomes necessary to draw out theadditional semicircle F on the protractor G in order to be able toadjust the scale It to the proper position.

The solution of right-angular trianglesis also greatly simplified by theaid of my compasses, and it is therefore particularly adapted todetermine the altitude of hills, edifices, poles, &c. The operationot'my compasses in solving right-angular triangles, however, isessentially the same as above described, and no further explanation willbe needed.

What I claim as new, and desire to secure by Letters Patent, is

The arrangement of the scales e,f, g, and h, in combination with themain semicircle O, and with the additional semicircle Fand protractor G,constructed and operating substantially as and for the purposespecified.

GEO. W. DICKINSON, JR.

Witnesses:

THos. E. DENIGAN, JOHN F. PEDIGO.

